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Communication is the transfer of meaningful information from the sender to the receiver.
- A: The information signal to be transmitted (Voice, music, DC to represent rudder position in Radio Control).
- B: Digitally compressed data. Analogue filtering and compression is possible too.
- C: The low power radio frequency carrier signal.
- D: The modulated carrier. The carrier has been modified in proportion to the signal to be transmitted.
- E: High power signal, usually radio, but light and ultrasound are common too.
- F: Attenuated signal. Energy is lost in the transmission medium. The received signal will most likely arrive with unwanted noise.
- G: Amplified signal.
- H: A low power copy of the original compressed signal.
- I: Ideally, an exact copy of the original information signal. There may be added noise, especially on analogue and AM systems.
The vast majority of communication systems include the following modules ...
- A device that converts a signal from nature into an electrical signal.
- For example a microphone for voice radio.
- Machine position sensors
- Robotic sensors
- Potentiometer used for position control
- Digital compression uses mathematical and statistical techniques (like making compressed ZIP files).
- Analogue compression modifies and filters the analogue signal to improve intelligibility.
- The carrier is a radio frequency sine wave on a precise frequency. This is the radio signal that gets transmitted.
- The carrier is needed because the transducer signal is usually on too low a frequency to be transmitted.
- The carrier is produced by an oscillator circuit.
- The frequency is often controlled by a quartz crystal.
- Baseband Communication transmits data without a carrier by sending the original signals into the cables.
- The carrier wave is modified by the signal from the input transducer. Common modulation methods include AM and FM.
- Digital modulation encodes information onto the carrier my altering its amplitude and/or phase.
- This is a power amplifier, used to boost the small signals above up to a useful power level for transmitting.
- Transmitter powers go from milliwatts for WiFi computer networks up to Megawatts for international radio broadcasting.
- Not all transmitters produce radio signals. A transmitter is needed to create the modulated light pulses for fibre optic links.
- Ultrasound is transmitted for imaging (foetus scan) and range finding used in top-end cars and by estate agents to measure room sizes.
- Free space
- Fibre optic
- Copper cable
- This contains sensitive amplifiers to pick up the transmitted signal.
- This is necessary because the transmitted signal is attenuated (loses energy) in the medium and becomes much weaker.
Demodulator / Decoder / Detector
- This retrieves the original signal from the modulated carrier.
- Ideally this can be done with no added noise or errors. Sadly this is rarely the case in real life.
- Reverse any analogue or digital compression used in the transmitter.
- Robotic devices
- Servo in a radio control model
- Computer processor in a wireless computer network
Full details are elsewhere on this site.
- AM - Amplitude Modulation used on LF, MF and the HF radio bands. (Long, Medium and Short Wave).
- FM - Frequency Modulation used on the VHF bands.
- DAB - Digital Audio Broadcasting on VHF.
- PAM - Pulse Amplitude Modulation
- PWM - Pulse Width Modulation
- PPM - Pulse Position Modulation
- PCM - Pulse Code Modulation
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